Study On Heat Transfer Characteristics And Calculation Method Of Shallow Underground Building Envelope

In recent years,urbanization has intensified.With the increasing thermal insulation of the building envelope,the building load caused by the heat transfer of the underground building envelope has become an increasingly important and non-negligible part of the total building energy consumption.Therefore,it’s essential for the accurate design of the underground building load and air conditioning system to make a more thorough analysis of the heat transfer process and characteristics between the underground structure and the earth,and further research on the load characteristics and energy consumption of the underground building.Numerical and analytical methods are mainly used in the research and calculation of the heat transfer of underground building envelopes in the current domestic and foreign literature,and relevant underground building design codes.Usually,the underground building is simplified as a one-dimensional or two-dimensional model,or the outdoor temperature is simplified as an astable sine wave（quasi-steady-state boundary）.However,the results obtained by these methods cannot be well combined with the actual engineering design.Given this situation,the research focus in this thesis is on finding the optimal design of the heat transfer calculation method of the underground building envelope.The outdoor hourly air temperature is used as the outdoor temperature in the simulation calculation,and a three-dimensional unsteady heat transfer calculation method for the underground building envelope is proposed.First of all,a three-dimensional unsteady heat transfer model of an underground building is established,and the finite volume method is used to solve it in MATLAB software.Taking the underground building in Jinan as an example,the heat flow and temperature field of its envelope structure are analyzed.The calculation results show that compared with the typical annual outdoor air dry bulb temperature curve,there is a delay of about 550 hours when the maximum value appears.In winter,the heat flow is mainly transferred from the underground building to the surrounding soil.And in summer,the heat flow is transferred from the soil to the outdoor surface.By comparing the two heat transfer calculation methods currently used and the simulation calculation results of FLUENT software,the superiority and accuracy of the proposed calculation method are tested.To further study the influence of different factors on the heat transfer of the underground building envelope,this thesis selects Jinan and Harbin as the representative cities in cold and severe cold regions.Change the design parameters such as the material of the outer wall of the underground building and its thermal insulation layer,the thermal physical property parameters of the soil area,and the aspect ratio of the underground building.Analyze the heat transfer characteristics of the outer wall of the typical underground building in two climate zones and the heat transfer characteristics of the outer wall of the typical underground buildings in different climate zones.The research results show that the amplitude of the annual heat flow curve through the underground building envelope is proportional to the soil thermal conductivity and inversely proportional to the soil thermal conductivity.The greater the aspect ratio of the underground building,the greater the index value of cold and heat caused by the envelope structure.For economical reasons,only the vertical envelope of underground buildings in severe cold areas can be thermally insulated in winter.Finally,to use the simplified method proposed in this thesis to calculate the peak cooling and heating loads of underground buildings under different types and working conditions without using software in the actual engineering design,the thesis proposes a concept for the nominal heat transfer coefficient of the outer wall of the underground building.And through a large number of examples,the fitting formulas of the nominal heat transfer coefficient under five working conditions are obtained.The accuracy of the nominal heat transfer coefficient fitting formula is verified by checking the mean square error and calculating with an underground building under certain conditions in Jinan City.The conclusions and the nominal heat transfer coefficient fitting formula obtained in this thesis provides a reliable and simple calculation tool for the design of cooling and heating loads of underground buildings in cold and severe cold regions,and have good reference value and guiding significance for practical engineering design.